The deficiency or low intestinal lactase activity that results in insufficient capacity or up to the incapacity to digest lactase, is rare as a congenital metabolic error, but it is a common syndrome in human adults. However, in most mammals there is a noticeable reduction of lactase activity from the moment of weaning. In humans whose ancestors have depended on a substantial consumption of milk or milk products for a long time, this reduction is less frequent. On the other hand, in unweaned babies, deficient or low intestinal lactase activity is rather infrequent.
The determination of intestinal lactase activity is important in pediatrics and gastroenterology and it can be carried out directly, from a sample of mucous membrane, or indirectly, from the level of sugar in the blood or from exhaled hydrogen, after administering a dose of lactase to the individual.
Direct determination has the disadvantage of being a complex and expensive method due to the fact that it requires special instruments and very specialized staff in order to remove the sample that should be subjected to analysis afterwards, aside from the fact that it is unpleasant and somewhat dangerous for the individual.
Other methods to determine intestinal lactase are based on the fact that disaccharides are, based on their affinity to lactase, capable of acting as a lactase substrate and they are converted, by action of the enzyme, into certain monosaccharides that are easily absorbed by the intestine and excreted in urine.
Spanish patent ES-P-9001680 describes the preparation of 4-O-β-galactopyranosyl-D-xylose disaccharide of formula (I)
for the evaluation of intestinal lactase activity. Said disaccharide is administered orally, acts as a substrate of intestinal lactase and therefore it decomposes in the intestinal tract, into xylose and galactose, the xylose being absorbed and excreted in urine, wherein xylose can be evaluated directly by means of a simple calorimetric method.
The amounts of xylose excreted in urine are correlated with the levels of intestinal lactase.
Spanish patent ES-P-9001680 also describes a method for basically preparing 4-O-β-galactopyranosyl-D-xylose, that comprises synthesis of benzyl β-D-xylopyranoside and that follows a sequence of operations that implies selective protection, glycosilation and deprotection reactions. The number of steps of the reaction, as well as the use of expensive reagents such as silver triflate in the glycosilation reaction, and the use of chromatography columns in the purification of intermediates and of the final product, produce costs and have difficulties to carry out this process on an industrial scale.
Spanish patents ES-P-9502185 and ES-P-9701156 describe enzymatic processes for the preparation of mixtures of galactopyranosyl-xylose disaccharides that contain the disaccharide (I) and its regioisomers 2-O-β-D-galactopyranosyl-D-xylose and 3-O-β-D-galactopyranosyl-D-xylose that, respectively, have the following formulae:

The processes described in Spanish patents ES-P-9502185 and ES-P-9701156 make it possible to obtain in a single reaction step and after chromatographic purification, mixtures of 2-, 3- and 4-O-β-D-galactopyranosyl-D-xylose useful as substrates and, therefore, for the determination of the enzymatic activity of intestinal lactase. Said processes, although feasible from accessible substrates and enzymes, have difficulties, from the point of view of industrial synthesis, for the characterization of the most suitable proportions, reproducibility of the preparation in said proportions and the determination of possible impurities.
On the other hand, Gorin et al. in “The Synthesis of β-Galacto- and β-Gluco-Pyranosyl Disaccharides by Sporobolomyces Singularis”, Can. J. Chem. 42(1964) 2307-2319, describe the synthesis of a plurality of disaccharides, among them 2-O-β-D-galactopyranosyl-D-xylose and 3-O-β-D-galactopyranosyl-D-xylose, by means of a process using cells. This publication does not describe any use of the different synthesized disaccharides.